Sanae Dekomori embodies an exuberant chuunibyou persona, marked by her dynamic energy and striking appearance. Her long blonde twin-tails, secured by weighted pouches she dubs "Mighty Mjolnir Maul," frame blue eyes and a petite 143 cm frame. She customizes school uniforms with frills, occasionally wearing her hair loose, and dons glasses for reading. Academically gifted, she mastered junior-high mathematics early and consistently leads her class. Though immersed in delusional roleplay, she consciously separates fantasy from reality, treating her antics as imaginative theater. Her speech quirks include ending sentences with "-desu," stylized as "death," reinforcing her dramatic flair.

Averse to dairy yet determined to grow taller, she grudgingly consumes milk daily. Born into affluence, she navigates life with a family butler and access to a luxury yacht for hosting gatherings. Her bond with Rikka Takanashi began in online forums discussing parallel worlds, evolving into a devoted "servant-master" dynamic. She idolizes the enigmatic "Mori Summer," clashing fiercely with Shinka Nibutani, whom she denounces as a fraud—unaware of Shinka’s genuine past as Mori Summer. Their rivalry simmers with public confrontations but conceals unspoken mutual respect.

Her narrative arc spans from junior-high eccentric to high school class representative and eventual student council president. In *Take On Me*, pragmatic instincts override her whimsy when aiding efforts to locate Rikka and Yuuta. Moments of vulnerability surface, such as tentatively acknowledging Shinka’s identity during elections, though her effusive praise backfires.

Distinctive details include hair accessories initially storing cookies, later swapped for candy, and a susceptibility to motion sickness. She values Yuuta Togashi’s acceptance of her chuunibyou traits and nurtures friendships within the Far Eastern Magic Napping Society of Summer, balancing loyalty and playful chaos.